Adhesives, or binders, are a necessary element of many absorbent products. While adhesives beneficially hold products together, they may also have a tendency to interfere with the absorption of fluid by the absorbent product because they are typically hydrophobic and/or non-absorbent in nature.
Hydrophilic adhesives are known. These adhesives are typically formulated from water-soluble polymers such as poly(vinyl alcohol), poly(vinyl methyl ether), poly(vinyl pyrrolidone), poly(ethylene oxide), or cellulose derivatives such as hydroxypropyl cellulose. Dextrans, starches and vegetable gums have also been used to provide hydrophilic adhesives. These materials provide adhesion under dry conditions. However, upon exposure to aqueous fluids, these materials lose bonding capability because they are substantially soluble in aqueous fluids.
A known approach for making hydrophilic adhesives more functional upon exposure to aqueous fluid is to crosslink water-soluble polymers. As a result of crosslinking, the material becomes swellable, and no longer soluble, in aqueous fluids. However, crosslinked polymers are difficult to apply to substrates or to establish intimate contact with surfaces because the crosslinked polymers are solid materials that have little or no ability to flow.
What therefore is needed is a hydrophilic binder composition or coating that has latent crosslinking capability. Such a binder composition could be easily applied, like a water-soluble polymer, since the hydrophilic binder composition would be capable of flowing prior to crosslinking. Latent crosslinking capability would also provide a simple means of crosslinking the binder composition after it has established intimate contact with a substrate or has formed a desired final shape or form.
One method for making such a binder composition includes a two-step process wherein monoethylenically unsaturated monomers, one of which contains alkoxysilane functionality, are polymerized and the resulting binder composition is then neutralized. The polymerization reaction is generally carried out in an organic solvent such as ethanol. Thereafter, crosslinking of the resulting binder composition can be moisture-induced by hydrolysis and condensation of the alkoxysilane during solvent removal.
Typically, the polymerization process of this method take about 6 to about 8 hours to complete followed by an additional period of time to effectively neutralize the resulting binder composition. Furthermore, this method requires the removal of the organic solvent, which may or may not be recovered.
There is thus a need for a method of making an absorbent binder composition that is faster. There is also a need for a method of making an absorbent binder composition that generates a lower level of organic waste. Furthermore, there is a need for an absorbent binder composition that is less expensive to prepare.